ASHRAE 62.1: A review of key requirements and concepts

ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality is the most commonly referenced standard to quantify acceptable conditions and appropriate HVAC system design.

Peter Alspach, PE, LEED AP BD+C, Arup, Seattle

07/15/2013

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Indoor air quality (IAQ) is probably the most commonly discussed aspect of building indoor environmental quality (IEQ). IAQ has direct effects on our health as well as the perception of an acceptable indoor environment. In the United States, ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality is the most commonly referenced standard to quantify acceptable conditions and appropriate HVAC system design. ASHRAE Standard 62.1 either forms the basis for most mechanical codes or is directly referenced by the codes themselves.

The standard is best known for its regulation of the amount of ventilation air delivered to each space by HVAC systems through its ventilation rate procedure approach to system design. However, the standard covers many other aspects of building design that are less well known and understood. The key aspects of building design that it covers are: outdoor air quality, envelope design and construction, HVAC system construction, concept of air classes, the ventilation rate procedure, the IAQ procedure, the natural ventilation procedure, and operations and maintenance.

Before getting into what the standard covers in detail, it is important to also understand what the standard does not cover. Standard 62.1 does not cover low-rise residential buildings and single-family dwellings—those are covered under the companion Standard 62.2. The standard also does not cover air quality in smoking areas, a change to the standard made in the 2010 update. Likewise in 2010 ventilation requirements for healthcare facilities were removed so that they could be solely referenced in ASHRAE Standard 170: Ventilation for Health Care Facilities. The other major areas that are not covered are the requirements for ventilation of industrial, laboratory, or other specific process driven ventilation requirements.

Outdoor air quality

Given the general approach within the standard of “dilution is the solution to pollution,” having good outdoor air quality is a very important premise when outdoor air is used as the “fresh” source to dilute the polluted indoor air. The standard requires two key pieces of information to perform the ventilation system design—demonstration of regional compliance with the National Ambient Air Quality Standards and the completion of a local survey of the specific project site. The survey is an important, and an often overlooked, aspect of the outdoor air quality. The survey is expected to focus on local sources of pollution—such as vehicular traffic—as well as other potential pollutant sources on adjacent properties such as boiler exhaust, process exhaust discharges, cooling tower discharges, and generator exhausts.

Outdoor air is required to be specially treated when the local conditions exceed the national standards. The standard focuses on outdoor air treatment of particulates and ozone. For high particulate areas, HVAC systems are required to provide varied levels of air filtration effectiveness (MERV 6 or MERV 11) depending on the whether the location is in particulate matter (PM) 10 or PM 2.5 noncompliance. For areas with ozone noncompliance, ozone removal systems must be installed. Luckily for most designers, there are only four locations listed that require ozone removal systems and they are all in California (Riverside, Kern, Los Angeles, and San Bernardino counties).

Envelope design and construction

Unbeknownst to many architects, ASHRAE 62 includes aspects of architectural design within its scope of requirements—it is not just a standard for mechanical engineers. It is important for mechanical engineering consultants and contractors to educate their architectural colleagues on those requirements. The architectural requirements generally focus on moisture management within the building enclosure to prevent or reduce the risk of mold growth within the building and include requirements for vapor and air barrier constructions.

While the architect generally relies on the engineer to identify air inlet and exhaust locations, the specification and detailing of the louvers associated with these functions is often by the architect (Division 8 per CSI). In particular, the standard has specific requirements for rain intrusion protection for louvered openings that need to be specified and considered when selecting louvers for a project.

The other major aspect of the standard that affects architects is the requirement for physical separation of certain spaces—particularly between parking garages and occupied spaces and smoking and nonsmoking areas.

HVAC system construction

Like the architectural requirements, much of the focus of the HVAC system requirements deals with moisture management within the system and its components. The main area of focus is on the requirements for drain pan construction and placement. Additional requirements govern the materials used for air conveyance (limiting material susceptibility to moisture damage and mold growth as well as erosion), coil design (limiting coil pressure drop where inadequate access is provided), and insulation requirements to prevent condensation on interior surfaces (noting that specific resistance values are not required—it is up to the designer to determine the required thermal resistance for the specific application).

Access for proper operations and cleaning is also important to maintaining equipment to allow for continued high levels of IAQ. While many of the requirements are common practice, it is worth reviewing the standard when designing or inspecting systems to ensure adequate access and cleanability is provided.